Computational investigations into hydrogen-atom abstraction from rhodium hydride complexes by methyl radicals in aqueous solution

Jason M. Keith; Dan Meyerstein; Michael B. Hall

doi:10.1002/ejic.201100825

Computational investigations into hydrogen-atom abstraction from rhodium hydride complexes by methyl radicals in aqueous solution

Jason M. Keith, Dan Meyerstein, Michael B. Hall

Department of Chemistry

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Abstract

The controversy in the reported kinetics for the hydrogen-atom abstraction reaction by methyl radicals for cis- and trans-[(Cyclam)Rh^IIIHCl] ⁺ and trans-[(Cyclam)(H₂O)Rh^IIIH]²⁺ has been resolved by studying several feasible mechanistic pathways with density functional theory. The only low-energy reaction mechanism predicted by these calculations involves a single-step radical-propagation mechanism in which the methyl radical simply abstracts the Rh bound H atom from the complex to form methane and the reduced Rh product. Previous experimental work on the chloride and aquo complexes suggested contradictory kinetic isotope effect (KIE) values of 0.66±0.30 and 1.42±0.07 as well as rate constants for the reaction differing by four orders of magnitude. The calculated mechanism predicts a KIE value of 1.08 and a high reaction rate. The alternative mechanisms are described briefly. The controversy in the reported kinetics for the hydrogen-atom abstraction reaction bymethyl radicals for cis- and trans-[(Cyclam)Rh^IIIHCl]⁺ and trans-[(Cyclam)(H ₂O)Rh^IIIH]²⁺ has been resolved by studying several feasible mechanistic pathways with density functional theory.

Original language	English
Pages (from-to)	4901-4905
Number of pages	5
Journal	European Journal of Inorganic Chemistry
Issue number	31
DOIs	https://doi.org/10.1002/ejic.201100825
State	Published - 1 Jan 2011

Keywords

Density functional calculations
Kinetics
Radical reactions
Rhodium

ASJC Scopus subject areas

Inorganic Chemistry

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10.1002/ejic.201100825

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title = "Computational investigations into hydrogen-atom abstraction from rhodium hydride complexes by methyl radicals in aqueous solution",

abstract = "The controversy in the reported kinetics for the hydrogen-atom abstraction reaction by methyl radicals for cis- and trans-[(Cyclam)RhIIIHCl] + and trans-[(Cyclam)(H2O)RhIIIH]2+ has been resolved by studying several feasible mechanistic pathways with density functional theory. The only low-energy reaction mechanism predicted by these calculations involves a single-step radical-propagation mechanism in which the methyl radical simply abstracts the Rh bound H atom from the complex to form methane and the reduced Rh product. Previous experimental work on the chloride and aquo complexes suggested contradictory kinetic isotope effect (KIE) values of 0.66±0.30 and 1.42±0.07 as well as rate constants for the reaction differing by four orders of magnitude. The calculated mechanism predicts a KIE value of 1.08 and a high reaction rate. The alternative mechanisms are described briefly. The controversy in the reported kinetics for the hydrogen-atom abstraction reaction bymethyl radicals for cis- and trans-[(Cyclam)RhIIIHCl]+ and trans-[(Cyclam)(H 2O)RhIIIH]2+ has been resolved by studying several feasible mechanistic pathways with density functional theory.",

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doi = "10.1002/ejic.201100825",

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AU - Meyerstein, Dan

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N2 - The controversy in the reported kinetics for the hydrogen-atom abstraction reaction by methyl radicals for cis- and trans-[(Cyclam)RhIIIHCl] + and trans-[(Cyclam)(H2O)RhIIIH]2+ has been resolved by studying several feasible mechanistic pathways with density functional theory. The only low-energy reaction mechanism predicted by these calculations involves a single-step radical-propagation mechanism in which the methyl radical simply abstracts the Rh bound H atom from the complex to form methane and the reduced Rh product. Previous experimental work on the chloride and aquo complexes suggested contradictory kinetic isotope effect (KIE) values of 0.66±0.30 and 1.42±0.07 as well as rate constants for the reaction differing by four orders of magnitude. The calculated mechanism predicts a KIE value of 1.08 and a high reaction rate. The alternative mechanisms are described briefly. The controversy in the reported kinetics for the hydrogen-atom abstraction reaction bymethyl radicals for cis- and trans-[(Cyclam)RhIIIHCl]+ and trans-[(Cyclam)(H 2O)RhIIIH]2+ has been resolved by studying several feasible mechanistic pathways with density functional theory.

AB - The controversy in the reported kinetics for the hydrogen-atom abstraction reaction by methyl radicals for cis- and trans-[(Cyclam)RhIIIHCl] + and trans-[(Cyclam)(H2O)RhIIIH]2+ has been resolved by studying several feasible mechanistic pathways with density functional theory. The only low-energy reaction mechanism predicted by these calculations involves a single-step radical-propagation mechanism in which the methyl radical simply abstracts the Rh bound H atom from the complex to form methane and the reduced Rh product. Previous experimental work on the chloride and aquo complexes suggested contradictory kinetic isotope effect (KIE) values of 0.66±0.30 and 1.42±0.07 as well as rate constants for the reaction differing by four orders of magnitude. The calculated mechanism predicts a KIE value of 1.08 and a high reaction rate. The alternative mechanisms are described briefly. The controversy in the reported kinetics for the hydrogen-atom abstraction reaction bymethyl radicals for cis- and trans-[(Cyclam)RhIIIHCl]+ and trans-[(Cyclam)(H 2O)RhIIIH]2+ has been resolved by studying several feasible mechanistic pathways with density functional theory.

KW - Density functional calculations

KW - Kinetics

KW - Radical reactions

KW - Rhodium

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Computational investigations into hydrogen-atom abstraction from rhodium hydride complexes by methyl radicals in aqueous solution

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